Brain perfusion is essential for life since the brain has a high metabolic demand. By means of cerebrovascular autoregulation the body is able to deliver sufficient blood containing oxygen and nutrients to the brain tissue for this metabolic need, and remove CO2 and other waste products.

However, due to the important influences of arterial carbon dioxide levels, cerebral metabolic rate, neural activation, activity of the sympathetic nervous system, posture, as well as other physiological variables, cerebral autoregulation is often interpreted as encompassing the wider field of cerebral blood flow regulation. This field includes areas such as CO2 reactivity, neurovascular coupling and other aspects of cerebral haemodynamics.

Brain perfusion in head trauma patients has been imaged using different techniques, including stable Xenon CT ^{1) 2)} and single photon emission computed tomography (SPECT)